1. Field of the Invention
This invention relates to a loop type data highway system in which various data-processing devices dispersedly distributed in a wide area are connected into a closed loop through a common bus and any one of these devices occupies the bus at any desired time so as to transfer information in series in a time division mode. More particularly, this invention relates to the art of data error check control in such a data highway system so as to improve the reliability of transmitted information and efficiency of transmission.
2. Description of the Prior Art
Various data highway systems of the loop type have been proposed heretofore as, for example, those disclosed in U.S. Pat. No. 3,639,904 invented by Jeganandaraj A. Arulpragasam, and U.S. Pat. No. 3,863,220 invented by A. Osawa et al. In connection with data transmission by way of such a loop type data highway system, various error detection methods have been proposed. One of the prior art methods comprises affixing an error check code to the end of a frame to be transmitted from a transmit station, transmitting the frame including the error check code to a receive station from the transmit station, and detecting an error, if any, in the receive station on the basis of the error check code. (Ref: W. W. Peterson "Cyclic Codes for Error Detection" Proc. IRE, Vol. 49, pp. 228-235)
According to this method, however, an error cannot be detected until the entire frame is received by the receive station. Thus, when, for example, an error occurs in the frame being transmitted, transmission of ensuing data is quite wasteful resulting in an undesirable reduction in the efficiency of data transmission.
Further, this error detection method is defective in that there is a probability of leaving an error undetected since this method uses an error check code generator, and that error detection becomes impossible when the length of the frame exceeds a predetermined limit. Therefore, the prior art error detection method is not suitable for application to a system which requires high reliability and a system which handles a large amount of data.